This invention relates to a calibration system for brake systems, and more particularly to a calibration system for brake systems used in stationary equipment such as medical rehabilitation devices and exercise equipment.
Known rehabilitation devices include a shaft that is coupled to a housing such that the shaft can rotate with respect to the housing. These known rehabilitation devices have a brake or a clutch that is coupled to the shaft. The brake or clutch is configured to apply different outputs, such as a force or a torque resistance, to the shaft to vary the amount of force or torque that is required to rotate the shaft with respect to the housing. In other words, the output applied by the brake or clutch is associated with the amount of torque that is required to be applied by a user to rotate the shaft with respect to the housing. Thus, because the amount of force required to be applied by a user to rotate the shaft with respect to the housing can be varied, a user may use the same rehabilitation device throughout an entire rehabilitation program. Additionally, users who are on different rehabilitation programs may use a common rehabilitation device.
In some of these known rehabilitation devices, an input signal, such as a voltage or a force, is supplied to the brake. The brake output applied to the shaft is based on the input signal that is received by the brake. In some known rehabilitation devices, a one-to-one relationship exists between a value of the input signal supplied to the brake and the value of the output produced by the brake. In other words, each input signal is uniquely associated with a single brake output. Additionally, the brake output is associated with the amount of torque that is required to be applied by a user to rotate the shaft with respect to the housing of the rehabilitation device. Thus, different input signals, such as different amounts of voltage, may be applied to the brake to vary the output produced by the brake, and to, therefore, vary the amount of torque required to rotate the shaft of the rehabilitation device with respect to the housing of the rehabilitation device.
Different brakes may vary slightly in the brake output that is associated with a given input signal. Additionally, individual brakes may change over time such that the brake output that is associated with a given input signal may vary. Thus, some of the known rehabilitation devices include calibrated brakes. A user of a rehabilitation device that includes a calibrated brake may select a desired threshold output value (the amount of torque required to be applied by a user to rotate the shaft of the rehabilitation device with respect to the housing of the rehabilitation device). The rehabilitation device will determine and apply to the brake the input signal necessary to more accurately produce a brake output so that the desired amount of torque rotates the shaft with respect to the housing.
Different known calibration methods have been used to calibrate the brakes of rehabilitation devices.
One method used to calibrate rehabilitation device brakes is an “average” method. The “average” calibration method includes determining, for a series of input signal values, average output values associated with the input signal values for a limited group of the rehabilitation device brakes (the test group). An equation is calculated based on the values of the input signals and the value of the average outputs for the test group. The equation, or a set of equations, is stored in a memory of each rehabilitation device, including rehabilitation devices that have brakes not included in the test group. The equation is subsequently used by the rehabilitation devices to determine the value of an input signal that is required to be applied to the brakes of the rehabilitation devices such that the a desired output is generated. Curve A of FIG. 1 is an example of an input-signal-value/output-value response curve using the “average” calibration method.
The “average” calibration method, however, does not include all of the brakes in the test group. In other words, when determining the average output values for the various input values, not all of the brakes are tested. In addition, any given brake will likely deviate from average, and this deviation may be significant from a performance perspective. All of the brakes, however, are calibrated with the same equation. Thus, the “average” calibration method does not provide for the differences of each brake, and therefore, can be inaccurate when determining the input signal required to be supplied to a specific brake so that the specific brake produces a desired output. Additionally, this method does not compensate for wear and other physical changes of an individual brake over a period of time.
Another calibration method is an “adjusted average” method. Unlike the “average” method each brake is calibrated individually in the “adjusted average” method. Specifically, the “adjusted average” method includes storing an average equation, or set of equations (calculated in the same way that the equation for the “average” method is calculated) in a memory of each brake system. Adjustment factors for each individual brake are then determined and stored in the memory of that individual brake system. The adjustment factors are calculated by supplying each brake with several input signals and determining the difference between the actual output of brake and the “average” output according to the average equation. Thus, the brake system may be programmed to apply the different adjustment factors of the individual brake to the average equation. Curve B of FIG. 1 is an example of an input-signal/output-value response curve using the “adjusted average” calibration method.
For example, for one brake, an adjustment factor of two (2) is applied to the average equation for inputs between a first input signal value and a second input signal value. Similarly, an adjustment factor of negative two (−2) is applied to the average equation for inputs between the second input signal value and a third input signal value. The “adjusted average” method, however, produces discontinuities in the input-signal-value/output-value response curve. Thus, the “adjusted average” method can be inaccurate about these discontinuities when determining the input signal required to be supplied to a brake so that the brake produces a desired output.
Thus, there is a need for a calibration method for a brake system that is specific to the individual brake and that is accurate, so as to not produce discontinuities or other inaccuracies in the input-output response curve.